The present invention relates to a vibration damping apparatus using a magnetic circuit, and more particularly to a vibration damping apparatus using a magnetic circuit suitable for being used as a component in a vibration damping apparatus, for instance, such as a suspension unit of a vehicle seat, a train seat, or a boat seat, an engine mount, and the like.
A variety of vibration damping materials, vibration dampers, and control techniques have been commonly used to reduce vibration and noise caused by a machine or an apparatus which itself is typically constructed of a low damping material in order to ensure its rigidity.
Damage to human body and its nervous system due to their exposures to vibration has become a serious problem with the ever-increasing vehicle speed. Such a damage shows many symptoms such as fatigue, headache, stiffness of shoulders, lumbago, and amblyopia. In general, vibration isolation is achieved by a damping apparatus with a properly matched spring such as metal springs or air springs and damping materials such as rubber, viscoelastic materials, or dampers. However, the dynamic magnification and the loss factor of the damping apparatus tends to be reversely related to each other. More particularly, a reduction in dynamic magnification to improve low-frequency characteristics of the damping apparatus tends to reduce the loss factor, resulting in the damping apparatus being too firm. An increase in the loss factor of the damping apparatus to improve high-frequency characteristics leads to an increase in its dynamic magnification, resulting in the damping apparatus being too soft and a poor damping efficiency at low-frequency. Many attempts have been made in the prior art to suppress vibration by semi-active control or active control or by using a passive damper containing a dynamic vibration damper.
A vibration damping apparatus containing a magnetic spring device, and having a spring constant being substantially pseudo-zero by incorporating a damping member or an elastic member such as a metal spring, a rubber material, has been recently disclosed. The present inventors have proposed a vibration damping apparatus using a variety of magnetic spring devices, and proposed a device in which a magnetic spring device and a shock absorber are provided together on a common link device to damp the vibration with the magnetic spring device while preventing contact with bottom members and the like by the damping force of the shock absorber for a large displacement accompanied by a large input vibration.
However, when a magnetic spring device and a shock absorber are provided together, the whole apparatus becomes large and a complicated structure. Therefore, it has been long hoped to develop a vibration damping apparatus which realizes both of a vibration damping function by a magnetic spring device and a damping function by a shock absorber in a simple construction so that the total structure can be made small.
On the other hand, the vibration damping devices hitherto proposed are only of one degree of freedom system to control vertical vibration or of 3 degrees of freedom system to be designed to control a horizontal vibration in fore-and-aft direction and right-and-left direction beside the above vertical vibration. A device containing also a shock absorber as described above has only one degree of freedom, and no proposal has been made for a vibration damping device to control the vibration having 6 degrees of freedom, that is, vibrations in X, Y, and Z axes directions in three dimensions and in a rotational direction around each axis in addition to the above directions, and being provided with a viscous damping function at the same time, in a compact design.
The present invention has been made to overcome the foregoing disadvantage of the prior art, and its object is to provide a vibration damping apparatus having a viscous damping function with a simple structure and making it in a small size. It is another object of the present invention to provide a vibration damping apparatus using a magnetic circuit, which is able to control a vibration having 6 degrees of freedom, to perform a viscous damping function when a large vibration is inputted and to make it in a compact structure.
To attain the aforesaid objects, the inventors first come up with the idea of constructing a magnetic spring device having one degree of freedom using a magnetic circuit which creates a negative spring constant in a predetermined range of the displacement amount in the axial direction and constructing a dash pot system using viscous liquid utilizing the casing of this magnetic spring device. The inventors also come up with the idea that by disposing a restoration device to restore a movable member to its original position from a displacement position in X and Y axis directions, that is, from a displacement position in other directions including a rotational direction, and an elastic member having a positive spring constant and enabling a combined spring constant in a predetermined range of the displacement amount to set to be substantially pseud-zero together with the above-described magnetic spring device, a vibration having 6 degrees of freedom can be controlled with a vibration damping apparatus thus structured in a compact structure.
That is, in a preferred embodiment of the present invention, a vibration damping apparatus using a magnetic circuit is provided. The vibration damping apparatus comprises:
a movable member disposed relatively movable along the axial direction in respect to a casing;
a movable magnet fixed on the movable member;
a stationary magnet fixedly disposed in the above casing, and forming a magnetic field to have a negative spring constant in a predetermined range of the displacement amount in the axial direction of the movable member with the movable magnet;
an elastic member to force the movable member in a direction to keep a distance away from the bottom wall of the casing, and to set a spring constant obtained by combining a magnetic force of a magnetic field formed by the movable magnet and the stationary magnet, and the elastic force to be substantially zero in a predetermined range of the displacement amount in the axial direction; and
a piston which moves by being pressed with the movable member and presses a viscous liquid filled in the casing to create fluid resistance when the displacement amount of the movable member in the axial direction reaches a predetermined value.
In a preferred embodiment of the present invention, a vibration damping apparatus using a magnetic circuit further comprises a restoration device to restore the movable member to the original position from the displacement position in other directions including a rotational directions other than the axial directions.
In a preferred embodiment of the present invention, the piston comprises a ring shaped net of a predetermined thickness, in which the outer peripheral face has an outside diameter possible to come in slidable contact with the inner peripheral face of the casing, and a circular shaped plate layered on the top and bottom faces of the net, wherein the net is deformed to to make the mesh smaller by a fluid pressure received by any circular shaped plate, when the movable member moves more than the predetermined amount in the axial direction in respect to the casing, and the mesh functions as an orifice to create fluid resistance.
In a preferred embodiment of the present invention, the net comprises a front mesh layer and a back mesh layer disposed at a predetermined distance, and has a three dimensional structure made by connecting each mesh layer to each other in a manner that a large number of piles are arranged in the opposing direction between the front mesh layer and the back mesh layer.
In a preferred embodiment of the present invention, the restoration device comprises a linkage member which abuts on the circumference of the movable member and displaces its position according to the displacement of the movable member in the other directions, and a rubber member disposed between the linkage member and the casing to allow the movable member to restore to the original position by the elastic restoring force.
In a preferred embodiment of the present invention, the restoration device comprises a linkage member which abuts on the circumference of the movable member and displaces its position according to the displacement of the movable member in the other directions, a first restoring magnet attached on the linkage member, and a second restoring magnet attached on the casing, wherein the first restoring magnet and the second restoring magnet are magnetized in a manner that the first restoring magnet and the second restoring magnet are forced to take positions always opposing to each other by their magnetic forces.
In a preferred embodiment of the present invention, the stationary magnets are disposed in the outside and inside of the movable magnet within the casing.
In a preferred embodiment of the present invention, the elastic member comprises a metal spring.
In a preferred embodiment of the present invention, a vibration damping apparatus using a magnetic circuit further comprises a ring shaped seal member connected to a movable cover fixed around a movable shaft composing the movable member, being able to support the movable cover at a predetermined distance from any of the members composing the casing, and having a function of limiting the movable range of the movable member in a downward direction by abutting on any of the members composing the casing, and a function to prevent leakage of the viscous liquid filled in the casing simultaneously.
In a preferred embodiment of the present invention, a vibration damping apparatus using a magnetic circuit further comprises a ring shaped seal member connected to a movable cover fixed around a movable shaft composing the movable member, being able to support the movable cover at a predetermined distance from any of the members composing the restoration device, and having a function of limiting the movable range of the movable member in a downward direction by abutting on any of the members composing the restoration device, and a function to prevent leakage of the viscous liquid filled in the casing simultaneously.
In a preferred embodiment of the present invention, a vibration damping apparatus using a magnetic circuit comprises
a movable member disposed relatively movable along an axial direction in respect to a casing;
an elastic member to force said movable member in a direction to keep a distance away from the bottom wall of said casing;
a piston which moves by being pressed with said movable member and presses a viscous liquid filled in said casing to create fluid resistance when the displacement amount of said movable member in the axial direction reaches a predetermined value; and
a magnetic circuit provided on the position opposing to said movable member and said casing, and generating a damping force created by the magnetic induction effect or by the electromagnetic induction effect accompanied by relative movement of said movable member to said casing.